In recent years, vehicle seat designs have become a very important vehicle marketing feature. Vehicle seats of increasing adjustability and functionality and improved comfort have added great complexity to the design process. Additionally, universal adjustment capability as well as Lumbar support adjustability features have increased assembly costs and further complicated design.
The desire for universal adjustability, Lumbar support features, and improved comfort and aesthetic appeal has contrasted with the general movement in the industry toward weight reduction for improved economy. Vehicle seat designers are now required to provide the above-referenced features while reducing weight of the seat assembly and without increasing manufacturing costs.
Typically, steel or aluminum seat frames are used in the seat assembly. In many current designs, an extruded aluminum tube is bent to form the seat back frame. Although aluminum frames can be lightweight, the range of back frame shapes available is limited. Moreover, the shape of back frame in conjunction with the hollow nature of the raw material steel or aluminum tube requires an expensive bending operation in order to avoid buckling or creating points of weakness in the bent frame.
Glass fiber and carbon fiber reinforced composite structures have high strength-to-weight ratios, carbon fiber composites particularly so. However, carbon fiber composites have generally been too expensive for use in vehicle seat back frames. Glass fiber composites are much less expensive than those reinforced with carbon fibers, however, the lower ends of the seat back frame contain both a pivot point around which the seat back pivots in the fore and aft directions, as well as an attachment point for the seat back adjusting mechanism. Glass fiber composites, unless made of heavy cross-section, cannot support the required loads at these points of stress concentration. Increasing the sectional thickness of a glass fiber composite frame would increase both the weight and the cost to the extent that such a frame could not compete with an aluminum frame.
Accordingly, it is desirable to provide a vehicle seat back frame with reduced weight, and with increased structural configuration ranges, without significantly increasing costs.